Metal supported glass window



Patented Apr. 15, 1947 METAL'SUPPOBTED GLASS WINDOW Daniel Alpert, Pittsburgh, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application March 29, 1943, Serial No. 480,990

3 Claims.

This invention relates to a metal supported glass Window, and particularly to a metal supported glass window for use in forming a vacuumtight seal.

In electrical systems involving the transmission of ultra high-frequency power through hollow waveguides, it is frequently necessary to maintain different parts of the system at difierent no direct transmission of power from the one part to the other but transfer of the power is accomplished by means of coupling loops. However, this arrangement is not entirely satisfactory, because of the necessity of providing impedance matching and tuning sections as well as the coupling loops. In addition such loops are difiicult to manufacture and assemble in the system.

pressures. For example, it is sometimes necessary thatone end of a wave-guide be connected v It is accordingly an object of my invention to a high vacuum tube while the other end opens to provide a novel window which may be eminto the antenna system at atmospheric pressure. ployed in forming a vacuum-tight seal while To enable different parts of the system to be permitting the passage therethrough of electromaintained at dilferent pressures, there must be magnetic radiation of an ultra-high frequency. a vacuum-tight vseal between these parts. The ,15 A furtherobject of my invention is to provide seal, in addition to being vacuum tight, must be a new metal supported glass window which may mechanically strong and electrically efficient. be employed in forming a vacuum-tight seal. The seal must not interfere unduly with the Another object of my invention is to provide transmission of the power. In most cases, it anovel metal supported glass window which may must not distort the ultra high-frequency waves be employed in forming a vacuum-tight seal and to any great extent, and power loss must be kept in which the glass is of uniform thickness. ata minimum. A still further object of my invention is to .Since glass passes ultra high-frequency power pr vid a w a d p v d metal supp rt d and is readily workable, attempts have been made gl s Window for 1158 in forming a Vacuum-tight to insert a glass window between the different S a Which is V y Strong mechanicallyparts of the system which are to be maintained Another object of my invention is to provide at different pressures. In one previously proa novel method of making a metal Supported posed arrangement, a glass window is formed glass Window Which y be p y in f m across the interior of a hollow wave-guide. How a vacuum-tight seal. ever, there are a number of difiiculties involved In accordance with my invention, .1 provide a in such an arrangement. Hollow wave-guides metal plate having an opening therethrough and and other apparatus for conducting ultra higha glass member filling the opening with a vacufrequency power must have highly conductive urn-tight glass-to-metal seal at the edges of the interior walls and are nearly always formed of opening between the glass member and the plate. copper. If a glass window is to be placed within The glass member may be of substantially unia copper wave-guide, there must be a vacuum form thickness and each surface thereof is preftightseal between the glass and metal. Thereerably in the same plane as the corresponding fore, some arrangement must be made for resurface of the plate. The glass member must, lieving the strains on the glass due to the differof course, have substantially the same coefficient ence in the coefiicient of expansion of the glass 40 of expansion over the range of temperatures to and. e ppe A glass seal formed in .a hollow be encountered as the metal plate. For this reawave guide under presently known methods is son, I prefer to form the metal plate Of an alloy rather thick and, as a result, the losses are high. which consists chiefly of iron, nickel and cobalt Moreover, the glass cannot be made .of uniform as described in detail in Patent 2.21'7,4-.2l, issued thickness so that the ultra high-frequency waves to Howard Scott on October 8, 1940. With the passing therethrough are somewhat distorted. alloy plate, I prefer to use a boro-silicate glass In addition, the glass seal within the wave guide of substantially the same coefficient of expandoes not have the necessary strength to withsion, such as Westinghouse 704 glass. The stand soldering and welding operations adjacent opening may be of any desired configuration, but thereto which may be necessary to complete the a circular opening is preferred because of the system. ease of manufacture, the high mechanical Because .of the many difficulties in providing strength, and the simplicity of calculations with a suitable glass seal in the transmission system, respect thereto when the article is to be used in thegeneralpractice in the artinvolves completely ultra high-frequency work. closing off one part of the system from the other In making the metal supported glass window,

I first provide an opening of the desired configuration in the metal plate. The edges of the metal at the opening are then rounded and oxidized. In some cases the edges need not be rounded to obtain satisfactory results. A piece of glass which preferably has a similar configuration as, but which is slightly larger than, the opening in the plate, is pressed into the opening while the glass is maintained at such a temperature that it is soft, and the edges of the metal plate at the opening are maintained at a temperature such that the oxide partially dissolves in the glass and the glass adheres to the metal. In this manner, a vacuum-tight glass-to-metal seal is formed at the edges of the opening.

While the glass in the opening is still soft, molten glass is added or subtracted therefrom until the glass in the opening has a substantially uniform thickness of the same order as the thickness of the plate. This may be accomplished by use of an auxiliary piece of glass. To add glass to that within the opening, the auxiliary piece of glass is heated until it is quite soft. The soft end of the auxiliary piece of glass is then allowed to fuse with the soft glass within the opening and that end remains therewith when the rest of the auxiliary glass is removed. To subtract glass from that within the opening, the auxiliary piece, while still cold, is placed against the soft glass within the opening. A portion of the glass within the opening then adheres to the auxiliary piece and may be removed thereby. By this method, the glass within the opening may be formed with a uniform thickness of il%. By turning the plate while the glass is soft to make use of the effect of gravity, the surfaces of the glass may be positioned in substantially the same planes as the corresponding surfaces of the plate if desired. Thereafter the plate and glass are permitted to cool. If a closer degree of uniformity is desired in the thickness of the glass, it may be obtained by grinding the glass after the plate and glass have cooled.

The metal supported glass window manufactured in the preferred manner described above has a number of advantageous features. As a seal is formed simultaneously at all edges of the opening with the same heat, an exceptionally good vacuum-tight glass--to-metal seal is provided. In addition the glass within the opening may be made comparatively thin with a substantially uniform thickness. For this reason, the metal supported glass window is particularly advantageous in ultra high-frequency systems for it permits power to pass therethrough with but very little loss and very little distortion or interference with the electromagnetic waves.

I have found that the metal supported glass window is also extremely strong mechanically. Not only may the glass be ground after the seal is formed, but the plate may also be machined. For example, holes may be drilled in the plate or the plate may be machined in a lathe without breaking the glass or destroying the vacuum-tight seal. I have also discovered that the plate may be soft soldered to other apparatus at any point up to the edge of the glass, and that it may be hard soldered or spot welded to other apparatus as close as one-sixteenth of an inch from the edge of the glass. Consequently, the plate may be conveniently secured to the end of a wave-guide to form a vacuum-tight seal through which power may be transmitted. Moreover, it is well. known that the presence of a solid dielectric, such as glass, within a conducting body effectively enlarges theinterior of that body as far as the transmission of ultra high-frequency power is concerned. Since the glass is within the opening in the metal plate, it effectively enlarges that opening. Therefore, if the plate is secured on the end of a section of the wave-guide, the opening may be of such size that there is very little interference with the transmission of power.

In making the metal supported glass window, I prefer to press into the opening in the plate a piece of glass having a similar configuration as, but which is slightly larger than, the opening. However, it is not necessary to use a piece having a similar configuration. Moreover, a piece of glass smaller than the opening may be employed although the glass-metal seal is not as uniform as in the preferred method. If a smaller piece of glass is employed, the opening is filled one section at a time. After the entire opening is filled with glass, the thickness of the window may be adjusted in the manner described in the preferred method.

If the glass having the proper coefficient of expansion for the supporting metal to be used has certain characteristics which are undesirable in the particular application of the window anticipated, a difierent glass may be employed to form the major portion of the window. For instance, Westinghouse 704 glass, while having the proper coeficient of expansion for use with the preferred alloy, causes a somewhat greater loss in the passage of ultra-high frequency power therethrough than Westinghouse 707 glass which does not have the proper coefficient of expansion. For applications in which the additional losses caused by the 704 glass are highly undesirable, I provide a metal supported glass window in which Westinghouse 704 glass is placed at the edges of the opening, forming a vacuum tight glass-to-metal seal, and Westinghouse 707 glass is in the central portion of the window and fused to the 704 glass at the edges. One method of making such a window is to follow the steps of the preferred method of making a window having but one type of glass while employing 704 glass until a seal is formed. Then glass is subtracted from the center of the window until only a rim of 704 glass remains. Thereafter 707 glass is added in the center in the usual manner (its edges being fused with the 704 glass rim. Because the glass to metal seal is strong and the joining point of 707 and 704 glass is strong, the strains in the glass set up by the difference in expansion of the 707 glass and the metal do not break the seal. Although the arrangement just described refers to 704 and 707 glass, these are merely illustrations and others may be employed if the necessary conditions are met.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. self, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

Figure 1 is an elevation view of a metal sup-.

ported glass window in accordance with my in vention;

Fig. 2 is a sectional view taken along line II- II of Fig. 1;

Fig. 3 shows a modified structure embodying my invention;

The invention it- "Fig. 4 is a sectional view taken along line IV-- IV of 3-; v

Figs. 5 and '6 show other modifications of my invention; and 7 Figs. '7 and 8 illustrate my invention as applied in an ultra high-frequency system.

As shown in Figs. 1 2, a metal plate 5 or disc has a circular opening therethrough which is filled withg-lass i. The edge of the metal at the opening is rounded as shown at and a vacuumtight seal between the glass Ti and metal 5 is presentat the edge of the opening. The metal plate 5 may be large or small, butit is preferably rather thin, of the order of 1010 to .020 inch when it is $9 e usedin an ul ra hig reque cy sy te T insure uniformity, the glass '5 is made of substantially the same thickness as the metal plate 5 with each surface of the glass in substantially the same plane as the corresponding surface of the plate.

In Figs. ;3 and 4, the metal plate 5 is shown as a narrow ring. The ring 5 is mounted within an opening in a second larger plate .i 3 and is secured therein by soft solder it. Thus, it is possible to have the larger plate l3 ,of a different material than the ring, and the soft solder takes care of the difference in expansion of the two materials. Sinceiit may bedesired to use a metal supported glass window in a number of diilerent applications, the window may be manufactured conveniently in quantity using the narrow ring as shown in Fig. 3 and then that ring may be secured to another larger piece of any desired shape and material.

Fig. 5 shows a modification of the metal supported window in which the window has a narrow substantially rectangular configuration which is particularly useful to polarize electromagnetic waves in a hollow guide.

Fig. 6 shows a window with a diiferent shaped opening. Both of the modified structures of Figs. 5 and 6 are manufactured in essentially the same manner as the structures shown in Figs. 1 and 2.

In systems involving the transmission of ultra high-frequency power through hollow waveguides, a number of difficulties have arisen in joining two sections of a wave-guide or in join-- ing various components of the system to a section of the wave-guide. To avoid the losses involved in a mechanical joint and the trouble involved in permanent electrical joints, choke-type joints are in general use which allow an excellent electrical joint without a correspondingly perfect mechanical joint.

The metal supported glass window described in connection with Figs. 1 through 6 may be advantageously employed in a choke-type joint as shown in Fig. 7. The choke comprises two members l1 and i8, one of which, ii, is mounted on the end of one section 59 of a wave-guide of circular cross-section while the other is mounted on the end of a second section 25 of the waveguide. The first member H is a relatively thick disc having an inner surface adjacent to the second member it. There is a central opening in the disc I! through which the end of the first wave-guide section it extends, the disc I! being soldered on the end of the wave-guide section IS. The disc I! has an annular slot or groove 2| in its inner surface which is parallel to the axis of the wave-guide it at approximately onequarter wave-length distance from the inner wall thereof, the groove being approximately onequarter wave length deep. The second member l8 of the choke is a metal plate having a central 6 opening .therethrough witha'glass member 23 po-f sitioned within the opening there being a vacuum-tight glass-to-metal sealat'the edge of the opening. The second section 25 of the wave guide is soldered to the plate l8. The inner surface of the disc i'l' abuts the inner surface of the plate it and bolts 2'! extend through the plate and disc outsideof the annular slot 2.! to increase the rigidity of the connection. The inner surface of the disc ll within the annular slot 21 is machined so that. a narrow space 2 exists between it and the adjacent portion'of the plate By virtue of the size and shape of the spaces at the choke type joint, very'little power is .lost. At the same time, by use of the apparatus shown Fig. 7, the di ferent'parts .of the .ultra highfreduency system may be conveniently 'maintained at different pressures. The metal supported glass window formed by plate !8 and member 23 not only enables a vacuum-tight seal to be made on the end of the second wave-guide section 25, but also serves as a part of the choke. The latter function of the'metal supported window is possible because the common surface of the plate '18 and the glass 223 permits the fitting thereto of themachined member I? of the choke without strain on the glass itself.

In Fig. 8, a metal supported window, formed of a metal plate 29 and a glass member 3|, is shown inserted between two sections 33 and 35 of a hollow waveguide. The end of each wave guide section is soldered to opposite sides of metal plate 3!. Such an arrangement may also be employed to advantage Where it is desired to maintain different sections of a wave-guide at different pressures. Obviously other windows such as the one shown in Fig. 5 may be mounted in this manner. The arrangement shown is possible because the wave-guide ends may be soldered to the plate closely adjacent to the glass without breaking the glass or disturbing the seal.

It is true that whenever there is a sharp discontinuity in the dimensions of a wave guide a large reflection of electromagnetic radiation may occur. However, inasmuch as the presence of an insulator, such as glass, within a metal opening enlarges the effective size of the opening with respect to transmission of electromagnetic radiation, the window size in an arrangement as shown in Fig. 8 may be made the same in effect as the wave guide itself although the guide is secured to the metal plate supporting the window. In this manner reflection of radiation is eliminated.

Although I have shown and described certain specific embodiments of my invention, I am fully aware that many modifications thereof are possible. My invention, therefore, is not to be restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. In combination, a metal body having a passageway therein, a metal plate having a peripherai shape of substantially the same outline as but sufiiciently smaller than that of said passageto permit said plate to be secured across substantially centrally within said passage- Way by soft solder in the space between the periphery of the plate and the walls of the passageway, said plate being so secured and having an opening therethrough, and a glass member filling said opening with a vacuum tight fused seal at the edges of said opening between said member and plate, said member having substan- 7 tially the same coefiicient of expansion as said metal plate and being located substantially within the boundaries formed by the planes of the surfaces of said plate.

2. In combination, a metal body having a passageway therein, a metal plate having a peripheral shape of substantially the same outline as but sufiiciently smaller than that of said passageway to permit said plate to be secured across and substantially centrally within said passageway by soft solder in the space between the periphery of the plate and the walls of the passageway, said plate being so secured and having an opening therethrough, and a glass member of substantially uniform thickness filling said opening within a vacuum tight fused seal at the edges of said opening between said member and plate, said member having substantially the same coefiicient of expansion as said metal plate and being located substantially within the boundaries formed by the planes of the surfaces of said plate.

3. In combination, a metal body having a passageway therein, a metal plate of substantially uniform thickness of the order of .010 to .020 inch and having a peripheral shape of substantially the same outline as but sufi'iciently smaller than that of said passageway to permit said plate to be secured across and substantially centrally REFERENCES CITED The following references are of record in the file of this patent:

I UNITED STATES PATENTS Number Name Date 2,075,477 Smith Mar. 30, 1937 2,057,452 Scott Oct. 13, 1936 2,227,511 Reynolds Jan. 7, 1941 2,219,573 Fraenckel Oct. 29, 1940 2,000,845 Jonas et al May 7, 1935 2,200,023 Dallenbach May 7, 1940 2,282,856 Engbert May 12, 1942 673,009 Poulson Apr. 30, 1901 2,089,541 Dallenbach Aug. 10, 1937 

